[tex]tg \dfrac{\pi}{4}+tg\dfrac{3\pi}{4}=\dfrac{tg\frac{\pi}{4}+tg \frac{3\pi}{4}}{1-tg \frac{\pi}{4}\cdot \frac{3\pi}{4}}=\dfrac{1 -1 }{1- 1\cdot (-1)}= \dfrac{0}{1+1} =\boxed{0}\\
\text{Formule folosite:}\\
\boxed{tg\ a+tg\ b=\dfrac{tg\ a+tg\ b}{1-tg\ a\cdot tg\ b}} [/tex]
